While it seems no longer necessary to emphasize the importance of recovering and employing solar heat, an article has recently appeared on June 8, 1975 in the New York Times dealing with this subject. This article generally points out that water or another liquid may be heated by the sun as the liquid passes through an appropriately disposed solar collector or panel with the heat being thereafter transferred to a storage facility such as, for example, water or rocks, this heat then being used when needed to heat domestic hot water and air that may be blown through a dwelling or other such construction. This article goes on to point out that all types of businesses were represented at the International Solar Industry Expo '75 and that there are high hopes for the solar industry especially as fuel costs continue to rise and as the populace grows more aware of pollution. It is pointed out that a survey had indicated that there will be a United States market of 1.3 billion dollars for solar heating and cooling systems by 1985 with a larger surge in potential sales during the following 15 years. The article points out moreover that black absorber panels have been employed into which is built a series of tubes filled perhaps with ethylene glycol acting as an anti-freeze although it in fact is known that water or some medium other than water or ethylene glycol can be employed to carry heat absorbed by the panel. In fact a wide variety of panels appear to have been developed all of which suffer certain disadvantages which will be discussed in greater detail hereinafter.
One of the problems encountered in the design of solar collector panels is that of corrosion in water based systems by virtue of the fact that water is employed for conveying heat collected by such panels to a heat storage system. Occasionally this problem can be avoided by chemical treatment of the water and by the use of deionized water and/or getter columns and so forth. Copper panels have the necessary corrosion resistance, but unfortunately such copper panels are heavy and expensive as compared to aluminum panels. Aluminum panels, on the other hand, have the necessary structural strength and the heat conductivity which is required, but aluminum by itself does not have sufficient corrosion resistance as to warrant its use in the form of a solar panel.
Olin Brass appears to have developed an aluminum Roll-Bond (trademark) solar collector panel which provides for the utilization of either aluminum or copper. This is accomplished by rolling sheets of copper or aluminum together and bonding the same and expanding the combined sheets in certain areas to form channels which permit fluid or refrigerant to be circulated. It is stated that the heat transfer characteristics of such a panel are excellent and enable a continuous and predictable rate of heating or cooling to be obtained from the associated system. I believe, however, that this system does not make for the most efficient use of materials. Where copper must be employed for corrosion resistance purposes in this system, it must be present in all areas including those which do not come in contact with the heat transfer fluid. This makes for an excessive usage of copper giving rise to increased weight and costs.
In preparing for the filing of a patent application, I have encountered various prior patents which do not effectively anticipate my invention, but should be mentioned for purposes of complete disclosure. Thus, for example, I am aware of the Kawano U.S. Pat. No. 3,081,825 which reveals a particular construction of a heat exchange element. In this patent a plurality of aluminum spacers are provided with wings which are made by cutting a tube along parallel lines. These fins and spacers are alternately inserted onto a copper tube whereafter a die of slightly greater outer diameter then the inner diameter of said tubes is mechanically forced therein. This mechanical force is applied sequentially throughout the length of the tube involved and in fact this tube is of relatively short length as are the fins and spacers employed in the aggregate assembly. The use of a mechanical force does not insure an intimate wedding of the materials, nor does it effectively resist the subsequent thermocycling of the assembly to which solar panels will be subjected. Furthermore, it will be noted in this patent that the assembly is of relatively short length relative to which the use of a mechanical die may be appropriate. However, where greater lengths are envisaged, of six feet or greater, the use of a mechanical die would not be appropriate.
I am also aware of Kawano U.S. Pat. No. 3,868,758. In this patent is revealed a method for manufacturing a finned tube as a heat exchanger. Herein a tube made of steel is covered with a thin wall pipe of aluminum having a high thermal expansion coefficient, good heat conductivity and softness. A number of fins are arranged in side-by-side relationship at fixed intervals on the outer periphery of a cylindrical member which is fixed on the thin wall pipe which covers the steel tube. The steel tube is expanded internally by passing a die therethrough, thereby causing the steel tube to press upon the interior surface of the thin wall pipe which expands and makes forced contact with the interior surface of the cylindrical member. This arrangement suffers all of the disadvantages of the other Kawano patent discussed above.
I am also aware of a number of other earlier patents which attempt to make use of multiple materials. These patents include Sandburg U.S. Pat. Nos. 2,722,732 and 2,732,615, Powell U.S. Pat. No. 2,646,259, Scott U.S. Pat. No. 2,311,579, Collura U.S. Pat. No. 3,464,402 and Duncan U.S. Pat. No. 3,089,480. None of these patents provide for an intimate wedding of aluminum and copper or other suitable materials in the manner of my present invention, nor do they provide for avoiding the consequences of thermal cycling such as solar panels are commonly subjected to. Furthermore, known techniques do not provide for the manufacture of solar panels by mass production techniques and in unlimited lengths while at the same time achieving the utilization of the best characteristics of different materials such as aluminum and copper or brass.